Aspects and embodiments of the invention are most generally directed to solid state optical devices, optical modulation devices, optical power conversion devices, optoelectronic conversion devices (including photovoltaic (PV) devices), and other optical devices that require both high optical transmission to and/or into an active region of the device, and electrical access, and most generally to any optical structure that makes use of electrodes in the optical path (all referred to hereinafter as ‘optical devices); more particularly, to optical devices having modified electrode characteristics and associated methods for increasing and/or optimizing the amount of light reaching an active region of the device where the light may be at least partially or completely absorbed, modulated, or at least partially transmitted, and applications thereof. The term ‘active region’ here signifies (or could, for example) a region of the device where light, possibly in combination with other factors (chemical, physical), can induce an electrically observable response, or where an applied electrical signal (voltage or current), possibly in combination with other factors (chemical physical), can induce a desired optical response. For example, getting light to the gap between electrode lines is advantageous for a modulator (for switching applications; absorbing light over some depth into the substrate beyond the electrodes is advantageous for optical detection). Apparatus and methods involving a wide range of electrode gaps and electrode sizes and enabling light transmission at frequencies ranging from the ultraviolet (UV) region through the infrared (IR) region are embodied by the invention.
In a broad variety of optical devices, incident radiation induces an electrical response, e.g., generating a current as the signal, a change in conductivity, or a change in current or, vice-versa; i.e., an electrical current or voltage changes the optical response. To detect or induce these responses, conductive contact materials may to be present. FIG. 1 shows a cross-section of a generic electrically addressable optical device, specifically a generic optical detector. Light (arrows A) is incident on the optical detector material (C) where it is at least partially transmitted and/or absorbed. This generic detector material may represent a wide variety of materials and structures, including but not limited to inorganic and organic semiconductors, semiconductor superlattices, semiconductors with embedded quantum dots, etc. An electrode (B) is present that can detect changes in electrical response. The electrode extends out of the plane of the figure and reaches an electrical circuit used for signal detection. A counter-electrode is present elsewhere on the device, typically at the bottom of the device or to the side of contact B. Contact B typically reflects and absorbs a significant fraction of the incident light, resulting in a shadowed region (D) and consequently a reduction in the amount of light that interacts with the detector material (C).
FIG. 2 shows a similar optical detector, where the presence of a positive electrode (B) and a negative electrode (E) is explicitly shown. The open detector area between the two electrodes is reduced compared to the total detector surface area, resulting in loss of detectable signal in the detection region C. The physical properties of the materials used and application-dependent technical requirements in some cases result in a relatively small fraction of open detector area, leading to large shadowing losses as shown at D and E. The embodied invention, in various aspects, reduces these losses and enables relatively more incident light to reach the light detection region of the device (e.g., substrate or active region of the substrate).
Several approaches to mitigate these shadowing effects, generally referred to as ‘transparent electrode’ structures, have been considered, including the use of transparent conductive oxides and periodically patterned electrodes resulting in plasmon enhanced extraordinary transmission. Transparent conductive oxides introduce appreciable optical absorption, and have conductivity values substantially less than metallic top contacts, respectively limiting device responsivity and device operation speeds. Periodically patterned electrodes that achieve optical transparency with the assistance of surface plasmons rely on interference effects, making them inherently narrowband and angle-dependent. Additionally they require micro-scale patterning.
In view of the shortcomings, challenges, and problems appreciated in the art, the inventor has recognized the benefits and advantages provided by one or more of the following attributes provided by the embodied invention:                improved transmission of light beyond the electrical contacts and reaching an active region of the device in optical devices that require electrical contacts on a top surface, resulting in better device performance;        no required patterning of the device material itself, avoiding deterioration of its physical, optical, and electronic properties;        no required regular electrode placement for electrodes much larger than the optical wavelength;        can be used for straight and curved electrodes;        no strong polarization dependence;        operable over a broad range of wavelengths (UV through IR);        compatible with common interdigitated electrode layouts;        used to potentially increase the amount of electrode material used with relatively little loss in light transmission, allowing low electrode resistance and potential or realized faster and more efficient (less resistive loss) device performance;        for small (diffraction regime) electrodes, makes use of surface plasmons on the electrode surfaces to further concentrate optical energy near the electrode gap;        for small electrodes and small electrode spacing, additional optimization of light redirection can be achieved by making use of diffractive effects caused by regular electrode placement.        